1. Field of the Invention
The invention relates to a high pressure membrane test cell of the type and particularly to a test cell having an upper, pressure chamber portion and a lower filter support portion detachably sealed together with a tangential fluid inlet to the pressure chamber and axial outlets from the upper and lower portions for the retentate and permeate respectively.
2. Brief Statement of the Prior Art
A cell of the above-mentioned type for membrane filtration and reverse osmosis has become known in practice. High pressure cells of this type are conventionally operated at pressures in the vicinity of 100 bar.
As compared with other known cells, the cell posesses the advantage of tangential inlet of the medium to be treated into a substantially conical pressure space. A central distributor with a conical foot prevents uneven central impingement of the membrane. The medium flows in a substantially spiral manner in the pressure space and is forced by the foot of the distributor through a narrow annular gap past the outer edge of the distributor foot into a very narrow disc-like space between the lower surface of the foot and upper side of the filter or of the membrane. From this position the medium leaves the pressure space as a retentate and the cell through a discharge duct arranged centrally and axially in the distributor, through a retentate discharge passage out of the cell. The permeate which has passed through the filter and the filter support leaves the cell through a permeate discharge formed in the bottom of the cell.
An important factor for obtaining reliable, reproducible data with this prior art high pressure membrane test cell is that the distance between the lower side of the distributor foot, at least in the marginal zone of the distributor foot, and the suface of the filter or of the membrane, is precisely reproducible for each treatment operation. This distance typically lies in a range of approximately 0.1 to 0.2 mm. This distance should also be precisely adhered to from one cell to another in order to be able to compare results obtained with different cells in a meaningful manner. These conditions are, however, not fulfilled with the prior art cell. Thus, the manufacturing tolerance is thickness of the porous sintered plate, which serves as a filter support, is greater by a facter of ten than the theoretically permitted tolerance of the gap width between the distributor foot and the filter. Furthermore, the distributor is extended in a integral manner through a hole on the top side of the upper part of the twopiece pressure cell and is connected in a sealing manner with the cell by welding. This method prevents any adjustment with the desired degree of accuracy of the relative position of the lower marginal part of the distributor foot. Finally, the upper part and the lower part of the prior art cell are connected in a sealing manner by intermediate rubber seals, which also lead to non-reproducible "drift in" spacing between the upper part and the lower part of the cell and accordingly between the lower edge zone of the distributor foot and the top side of the filter. This in turn causes non-reproducible and unreliable results over an extended period of time with respect to one and the same cell.